This invention is related to the side-view mirror of automobiles, particularly to the elimination of the blind-spot hazard related to such mirrors.
For automobiles driven in the United States, it is the standard practice to have a planar mirror for rear view, a curved mirror for the right-side view, and a planar mirror for the left-side view. A number of inventions of the past reflect the development of mirrors for these purposes. For example, a rear-view mirror comprising a plane glass sheet silvered in the rear, U.S. Pat. No. 1,808,740 issued to Weatherbee, functions alternately during day or night through a mechanical switch. Another form of rear-view mirror that comprises a plurality of vertical mirror strips of progressively varying inclination, the inclination increasing in opposite directions from the center toward the outer edges was patented by Gray vide U.S. Pat. No. 3,806,232. The strips comprising such a device are so positioned relative to one another that in combination, they provide the result of a curved mirror. The curved side-view mirror generally used for right-side view presents to the driver an unrealistic perception of image distance, a well-known hazard. On the other hand, the mirror of the planar type used for left-side view presents a different hazard; that of leaving a blind spot. A wide mirror could remedy this, but use of large mirrors that project excessively to the outside need to be avoided. This led to the use by some drivers of a small separate curved mirror to be attached within the front surface of the conventional side-view mirror. Such an arrangement is however not convenient for viewing, and additionally is cause for the incorrect perception of distance that is characteristic of curved mirrors. Recently, however, side-view mirrors that avoid the blind spot have been invented. Jose C. Palathingal presented such a side-view mirror under U.S. Pat. No. 5,838,505. A device of potentially greater longevity and ease of manufacture was subsequently patented by Jose C. Palathingal, vide U.S. Pat. No. 6,074,068. These new devices however generate two separate images for the entire field of view, and may cause confusion to drivers, especially in a major highway with several lanes.
The aim of the present invention is an improved version of a side-view mirror for the left that avoids the hazard of the blind spot without introducing a curvature in the mirror configuration, and also avoids a possibility of driver confusion in a multilane major highway.
The present invention is developed consequent of closely investigating the blind spot and studying the distinct separate regions of view presented to the automobile driver by the upper and lower parts of a vertically fixed side-view mirror under driving conditions. Careful observation of the functioning of the mirror will show that whereas the upper part of the mirror directs the view of the driver approximately horizontally backward toward large distances, the lower part of the mirror leads to a downward view of a rear region of the road closest to the automobile. This can be seen from FIGS. 1(a) and 1(b) representing prior art. The mirror used herein, marked 40 is of the conventional planar type, of size roughly 6xe2x80x3 width and 3.5xe2x80x3 height. It is assumed that the driver eye, marked 50 is positioned at a distance approximately 30 inches from the mirror, at a height roughly 6 inches above the top of the mirror. For simplicity of discussion, only one eye of the driver is considered. As illustrated in FIG. 2, the mirror is mounted nearly vertically at 72xc2x0 inclination in the horizontal plane to the dashed line 30 drawn horizontally, representing the vertical plane grazing the left side of the auto. Line 30 is hereinafter referred to as the auto left-side line. In this geometry, rays of light reflected from the mirror in directions having inclinations between 36xc2x0 and 48xc2x0 to the auto left-side line 30 are directed toward the driver eye 50. In FIGS. 1(a) and 1(b), it is illustrated that near-horizontal rays 42 and 46, the former traveling at little inclination to the auto left-side line 30, and the latter traveling at 12xc2x0 inclination in the horizontal plane to line 30, reflected from the upper sector of the mirror, are directed toward the driver eye. Horizontal rays can thus be reflected by the mirror into the driver eye positioned at a greater height because in normal use, the orientation of the mirror is adjusted by the driver to provide an upward angular tilt of roughly 5xc2x0 to 10xc2x0 by rotation about a horizontal axis. Rays 52 and 56, originating from a point on the road in the vicinity of the auto, and traveling at inclinations approximately 0xc2x0 and 12xc2x0 respectively to the vertical plane of the auto left side, are reflected from the bottom sector of the mirror toward the driver eye. FIG. 2 illustrates that rays of light 32 and 36 of unspecified points of origin are reflected along paths 34 and 38 toward the driver eye 50 at inclinations 36xc2x0 and 48xc2x0 respectively to line 30. Thus it becomes clear that the visual range of the driver for side view on the road on the left of the auto is 0xc2x0 to 12xc2x0 to the auto left-side line 30. The close-by region seen on account of the lower one-third of the mirror surface enables view of the section of the road of a rear distance ranging typically from 30 feet to 50 feet from the mirror. The road surface in the left rear at distances shorter than 30 feet do not come into view. The estimates of distances are not expected to be accurate because they depend on a number of assumptions and approximations. The upper two-third of the mirror provides view beyond 50 feet, extending toward the horizon. An extraneous vehicle 110 approaching from large distances can be seen by the driver of the vehicle 100, hereinafter called the primary vehicle, on account of the upper part of the mirror 40. As the extraneous vehicle comes within 50 feet, it becomes visible through the lower part of the mirror. Since the directional range of view is about 0xc2x0 to 12xc2x0 on the left, the road width the driver of vehicle 100 can see sideways is 6 feet at a road distance 30 feet behind and 10 feet at 50 feet behind. Assuming that the extraneous vehicle 110 keeps a side distance of roughly 6 feet from the primary vehicle 100, the vehicle 110 becomes invisible to the driver of vehicle 100 as vehicle 110 arrives closer than about 30 feet behind the driver of vehicle 100. The extraneous vehicle has to advance further and be within about 5 behind the driver of the primary vehicle before it could be seen by the driver through peripheral eye vision. Thus, the range of road distance in the lane left of the primary vehicle toward the rear, 5 to 30 feet could be roughly defined as the blind spot.
The considerations discussed above suggest that, in order to obtain a view of the blind spot, the lower part of the mirror needs to be altered, whereas the upper part is left to be of the conventional single-planar type. In the mirror of the invention, the lower part of the mirror shall provide the automobile driver with one or more directional ranges of view different from the directional range provided by the upper part. The view so provided by the lower part shall include the region of the blind spot mentioned above and illustrated in FIG. 2.
The present invention is a rectangular mirror that comprises a transparent plate, one side of the plate being single-planar. The opposite side of the plate comprises two sectors, one sector that is planar and another that is zig-zagged. In a preferred embodiment, one side of the plate is single-planar. The opposite side comprises a planar sector and a zig-zagged sector. In this embodiment, with the mirror fixed vertically, the planar side of the mirror plate forms the frontal surface whereon light is incident. The opposite side forms the rear, and the zig-zagged sector is below the planar sector. The zig-zagged sector comprises a plurality of series of surface strips, each series being constituted of strips identical in shape and surface area, mutually parallel, and inclined at a predetermined angle relative to the single-planar front surface. The angle of inclination of the surface strips is distinct for each series. The surface strips of the different series alternate periodically in an orderly sequence so that the zig-zagged surface is comprised of a plurality of identical zig-zag elements formed of a plurality of surface strips, with intervening angles between adjacent surface strips repeating periodically. The number of zig-zag elements comprising the zig-zagged sector may vary in different embodiments. Yet, a large number of zig-zag elements helps reduce the zig-zag amplitude, marked 18 in FIG. 3(b), and hence avoid a large variation in thickness across the mirror surface.